Abstract:

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Fully dense composite materials of M3/2 high speed steel reinforced with 5, 10 and
15vol. % of high purity niobium carbide were developed using powder metallurgy processing. This
work describes and discusses the mechanical behavior of the various composite systems.
Mechanical properties were characterized by Rockwell hardness, compression and three point
bending tests. It was found that the addition of ceramic particles causes a very small increase in the
hardness and 0.2% yield strength, but a decrease in the transverse rupture strength is observed. In
order to eliminate the influence of martensite on the mechanical properties, measurements were also
conducted after tempering. After this treatment, the reinforced materials showed a moderate yield
stress increase at room temperature respect to the unreinforced M3/2. However, the bend strength
values were not affected significantly by this treatment. At high temperatures, the addition of
reinforcement particles causes a slight increase in the strength. Strain rate-change tests in
compression were performed at strain rates ranging from 3 x 10-6 to 2 x 10-3 s-1 in the temperature
range from 650 to 750°C. The deformation behaviour was characterized by a stress exponent
ranging from 5 to 7 and an activation energy for plastic deformation similar to that found in high
alloyed ferritic steels.

Abstract: The molybdenum powder doped with rare earth oxide was processed by powder metallurgy method and a new style thin film cathode material was firstly processed by Spark Plasma Sintering (SPS) method in this paper. The secondary emission property of such kind of cathode materials were studied, the maxim secondary emission coefficient after the material was activated at 1600°C reached to 3.84 about
double that of traditional cathode materials application in magneto. The microstructure, element analysis and phase constitution of materials before and after the secondary emission property was measured were studied through SEM, EDAX and XRD. The results show that a rare earth layer about 5um thickness was
created after the material was activated at 1600°C. The material grain size is about 1 um or even smaller and the distribution of elements in such materials is even.

Abstract: Nanocomposite tool materials are very important in engineering field for their advantage
in mechanical properties and have a good foreground in the coming years. However, there are lots
of puzzles in the materials design theory. So in this paper, a new nanocomposite tool materials
design method is proposed based on the interface debonding theory. The wild phase content can be
fixed by calculating the debonding interface rate and the strength requirement of the tool materials.
Therefore, an experiment is carried out to fabricate WC based nanocomposite tool materials under
the guider of the interface debonding theory. Results show that the experimental data is in
accordance well with the calculation and the model is proved to be correct.

Abstract: The Cu-based friction materials with nano-graphite were prepared through powder metallurgy technology. The microstructure and friction performance were studied through scan electronic microscope (SEM) and friction tester, respectively. The results indicate that coefficient of the Cu-based friction materials with 2 wt% nano-graphite is high and stable. Comparing with the friction materials without n-C, the wear resistance and heat resistance of the friction materials with nano-graphite has been improved by 11 % and 25 %, respectively. The nano-graphite particles will reduce the abrasive wear and enhance the wear resistance of the Cu-based friction materials.

Abstract: Engineering materials with better high temperature oxidation properties are needed to increase the thermodynamic efficiencies of the energy production and transportation systems. Because of their high melting temperatures, refractory metals like Nb or Mo are brought together with intermetallic compounds as two components of a new class of composite materials. To acquire a balanced high temperature mechanical and oxidation properties, these materials generally have multiphase and multicomponent structures. Borides of some transition elements are also being considered as high temperature structural materials for new aerospace vehicles. These materials are also required to have sufficient high temperature oxidation resistance in order to provide reliable and long service lives.

Abstract: The precipitation and dissolution behavior of niobium carbo-nitrides is of particular interest for many technical applications. Niobium-microalloyed high strength low alloy (HSLA) steels are widely used in civil construction, automobile and line pipe applications. These steels rely on thermomechanical processing. In this context, coupled processes like thin slab casting and thermomechanical rolling of microalloyed steel grades require most precise information on the precipitation state at the individual processing steps.
Reasonable equations for the solubility product at thermal equilibrium can be taken from literature but kinetics is largely unknown. Conventional X-ray technology is not able to detect small volume fractions below 0.1% of nanoscale precipitates. Investigation of nanoscale niobium precipitates by transmission electron microscopy (TEM) analysis or chemical extraction methods is common practice. However, TEM suffers from statistical relevance and chemical extraction will not give information on particle distribution and orientation.
Investigation by high energy synchrotron X-ray of about 100 keV offers statistical relevance as volumes of several cubic millimeters are regarded. This large reflecting sample volume allows to detect nanometer-sized particles and provides very high angular resolution leading to an exact determination of the reflection peaks. The wavelength of around 0.12 Å is able to analyze nanometer-sized particles. Due to the high energy of the applied synchrotron radiation, precipitation and dissolution reactions could be observed during thermal treatment inside a soaking furnace. The results establish this technology for analysis of nanoscale niobium carbo-nitride precipitates